This is a divisional application of application Ser. No. 11/805,056 filed on May 22, 2007 now U.S. Pat. No. 8,030,733 by Abdalla Aly Naem.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuse target and, more particularly, to a copper-compatible fuse target and a method of forming the copper-compatible fuse target.
2. Description of the Related Art
A fuse is a device that provides a low-resistance current path between two conductive lines when the fuse is unprogrammed, and a high-resistance current path between the two conductive lines when the fuse is programmed. Fuses are commonly used to trim semiconductor devices, such as resistors, to form precision analog devices.
A fuse target is a device that has a unique signature which can be detected by an optical recognition system. For example, an optical recognition system can detect the shape and reflectivity of a fuse target, and then determine the position of the fuse target. The fuse target has a known positional relationship with respect to the semiconductor fuse. As a result, the position of the semiconductor fuse can be determined from the position of the fuse target.
FIGS. 1A-1C show views that illustrate a prior-
art semiconductor wafer 110 with a fuse and a fuse target.
FIG. 1A shows a plan view, while
FIGS. 1B and 1C show cross-sectional views taken along
line 1B-
1B of
FIG. 1A. As shown in
FIGS. 1A-1C,
semiconductor wafer 110 includes a
semiconductor substrate 112 and a
metal interconnect structure 114 that is connected to
semiconductor substrate 112.
Semiconductor substrate 112 includes a number of structures that are formed in and on
substrate 112. The structures, which include resistors, transistors, capacitors, diodes, and similar devices, have a number of
conductive contact regions 112C, such as the ends of a resistor and the terminals of a transistor. In the present example, the resistors include a trim resistor that has a first polysilicon resistive segment RS
1 with a
conductive contact region 112C at an end RE
1, and a second polysilicon resistive segment RS
2 with a
conductive contact region 112C at an end RE
2.
Metal interconnect structure 114, in turn, is a multi-layered structure that electrically interconnects together the various devices that are formed on
substrate 112 to realize an electrical circuit.
Metal interconnect structure 114 includes a number of
contacts 114C that touch the
conductive contact regions 112C (either directly or via silicide).
Metal interconnect structure 114 also includes a number of metal-1 traces
114-M
1 that are connected to the
contacts 114C, a number of metal-2 traces
114-M
2, a number of metal-3 traces
114-M
3, and a number of metal-4 traces
114-M
4. In the present example, the metal-1 traces
114-M
1, the metal-2 traces
114-M
2, the metal-3 traces
114-M
3, and the metal-4 traces
114-M
4 are implemented with aluminum. Further, selected regions on the top surfaces of the metal-4 traces
114-M
4 are exposed to the external world, and function as
bond pads 114P that provide an external electrical connection point.
In addition,
metal interconnect structure 114 includes a number of
inter-metal vias 114V that connect the metal-1 traces
114-M
1 and the metal-2
114-M
2 traces together, the metal-2 traces
114-M
2 and the metal-3
114-M
3 traces together, and the metal-3 traces
114-M
3 and the metal-4
114-M
4 traces together.
Metal interconnect structure 114 further includes a planarized
insulation region 114I that touches
semiconductor substrate 112, the
conductive contacts 114C, the metal-1 traces
114-M
1, the metal-2 traces
114-M
2, the metal-3 traces
114-M
3, the metal-4 traces
114-M
4, and the
inter-metal vias 114V. In the present example,
insulation region 114I includes a region of
oxide 114L and an
overlying passivation layer 114U.
Passivation layer 114U, which has a
top surface 114S, can be implemented with, for example, oxide, nitride, or a combination of oxide and nitride.
Metal interconnect structure 114 further includes a
fuse 116 which has a first end FE
1 and a second end FE
2. First end FE
1 makes an electrical connection with the structure to be trimmed which, in the present example, is end RE
1 of polysilicon resistive segment RS
1 of the trim resistor. Similarly, second end FE
2 makes an electrical connection with the structure to be trimmed which, in the present example, is end RE
2 of polysilicon resistive segment RS
2 of the trim resistor.
Fuse 116 is illustrated in the present example as a short thin metal-2 trace, although
fuse 116 can be implemented in other metal layers.
In addition,
metal interconnect structure 114 includes a stacked metal ring structure MR
1 that is formed around
fuse 116 to protect adjacent regions of
wafer 110 from
fuse 116 during programming. Metal ring structure MR
1 includes a metal-1 trace
114-M
1 that is formed around
fuse 116 as a metal-1 ring M
1R
1, and a metal-2 trace
114-M
2 that is formed around
fuse 116 as a metal-2 ring M
2R
1. Further, metal ring structure MR
1 includes a metal-3 trace
114-M
3 that is formed around
fuse 116 as a metal-3 ring M
3R
1, and a metal-4 trace
114-M
4 that is formed around
fuse 116 as a metal-4 ring M
4R
1.
The metal rings M
1R
1, M
2R
1, M
3R
1, and M
4R
1 are electrically connected together by way of a number of
inter-metal vias 114V, but are electrically isolated from all other conducting structures. (Only one
fuse 116 is shown for clarity. A large number of
fuses 116 can lie within stacked metal ring MR
1 (a bank of fuses), and
wafer 110 can include a large number of fuse banks.)
Metal interconnect structure 114 also includes a
fuse opening 118 in planarized
insulation region 114I that exposes a
thin layer 114T of planarized
insulation region 114I that lies on
fuse 116.
In addition,
metal interconnect structure 114 includes a
fuse target 120 that has a known positional relationship with
fuse 116. (Only one
fuse target 120 is shown for clarity. Fuse targets are commonly located in the corners of a region that surround the fuse banks.) In the present example,
fuse target 120 is illustrated as an exposed, electrically-isolated, L-shaped metal-4
trace 120M that sits on a
pedestal 122 surrounded by a
trench 124.
Metal interconnect structure 114 further includes a stacked metal ring structure MR
2 that is formed around
fuse target 120 to protect adjacent regions of
wafer 110 from
fuse target 120 during the formation of
fuse opening 118 and
trench 124. Metal ring structure MR
2 includes a metal-1 trace
114-M
1 that is formed around
fuse target 120 as a metal-1 ring M
1R
2, and a metal-2 trace
114-M
2 that is formed around
fuse target 120 as a metal-2 ring M
2R
2.
Metal ring structure MR
2 also includes a metal-3 trace
114-M
3 that is formed around
fuse target 120 as a metal-3 ring M
3R
2, and a metal-4 trace
114-M
4 that is formed around
fuse target 120 as a metal-4 ring M
4R
2. The metal rings M
1R
2, M
2R
2, M
3R
2, and M
4R
2 are electrically connected together by way of a number of
inter-metal vias 114V, but are electrically isolated from all other conducting structures.
In operation, in the native or unprogrammed state, which is shown in
FIG. 1B,
fuse 116 provides a low-resistance current path between the resistive segments RS
1 and RS
2. To
program fuse 116, an optical recognition system is used to detect the shape and reflectivity of
fuse target 120, and then determine the position of
fuse target 120. Once
fuse target 120 has been located, the position of
fuse 116 is determined from the known positional relationship.
After the position of
fuse 116 has been determined, a laser beam with a predefined output power is directed to that position.
Fuse 116 is heated by the laser until a portion
thin insulation region 114T and a portion of
fuse 116 evaporate away to leave two physically separated sections of
fuse 116. The two physically separated sections of
fuse 116, in turn, provide an open current path between the polysilicon resistive segment RS
1 and RS
2.
FIG. 1C shows
semiconductor wafer 110 after
fuse 116 has been programmed.
One problem with
fuse target 120 is that
fuse target 120 is not compatible with the current-generation processes that are used to form copper-topped interconnect structures. To reduce the resistance of a metal interconnect structure, current-generation processes commonly form the top one or more layers of metal traces from copper.
FIGS. 2A-2G show a series of cross-sectional views that illustrate a prior-
art method 200 of forming copper traces that lie over a top layer of aluminum traces. As shown in
FIG. 2A,
method 200 is practiced on a conventionally-formed
semiconductor wafer 210 that includes an interconnect structure which has a top layer of aluminum traces
212.
As further shown in
FIG. 2A, the method begins by depositing a layer of passivation (non-conductive)
material 214, such as a layer of nitride, oxide, or a combination of oxide and nitride, over the top surfaces of the aluminum traces
212. The method continues by forming and patterning a
mask 216 on
passivation layer 214. Following this, the exposed regions of
passivation layer 214 are etched to form
openings 220 that expose the top surfaces of the aluminum traces
212 of the interconnect structure.
Mask 216 is then removed.
As shown in
FIG. 2B, after
mask 216 has been removed, a
seed layer 222 is formed on
passivation layer 214 and the exposed regions of the aluminum traces
212.
Seed layer 222 typically includes a layer of titanium (e.g., 300 Å thick) and an overlying layer of copper (e.g., 3000 Å thick). The titanium layer enhances the adhesion between the underlying aluminum traces
212 and the overlying layer of copper. Next, a
mask 224 is formed and patterned on
seed layer 222 to have a number of
openings 226 that expose the number of
openings 220.
As shown in
FIG. 2C, following the formation and patterning of
mask 224, copper is electroplated to form a number of copper traces
230 which each has a
top surface 230T.
Mask 224 and the
seed layer 222 that underlies
mask 224 are then removed. Next, as shown in
FIG. 2D, a
sealant 232 that is resistant to humidity and corrosion, such as cobalt or nickel, is deposited over
passivation layer 214 and the copper traces
230. A
mask 234 is then formed on
sealant 232. The exposed regions of
sealant 232 are then removed from the top surface of
passivation layer 214 to form a number of sealed copper traces
236. Each sealed
copper trace 236, in turn, has a
top surface 236T.
Mask 234 is then removed.
Alternately, as shown in
FIG. 2E,
mask 224 can be removed, followed by the deposition of
sealant 232 over
seed layer 222 and the copper traces
230.
Mask 234 is then formed as above. After this, the exposed regions of
sealant 232 and the
underlying seed layer 222 are removed from the top surface of
passivation layer 214 to form the sealed copper traces
236.
Mask 234 is then removed.
Next, as shown in
FIG. 2F, a layer of non-conductive material (e.g., benzocyclobutene (BCB) or a polymer)
240 is deposited on
passivation layer 214 and the sealed copper traces
236. After
non-conductive layer 240 has been deposited, a
mask 242 is formed on
non-conductive layer 240. Following this, the exposed regions of
non-conductive layer 240 are etched to form
openings 244 that expose selected regions on the top surfaces of the sealed copper traces
236.
Mask 242 is then removed.
As shown in
FIG. 2G, after the
openings 244 in
non-conductive layer 240 have been formed, a
metal layer 250, such as aluminum or gold, is deposited on
non-conductive layer 240 to fill up the
openings 244 and contact the selected regions on the top surfaces of the sealed copper traces
236. After this, a
mask 252 is formed and patterned on
metal layer 250. Next, the exposed regions of
metal layer 250 are etched to form a number of
metal bond pads 254.
Mask 252 is then removed. After
mask 252 has been removed, solder balls can be attached to the
metal bond pads 254 or, alternately, thin wires can be bonded to the
metal bond pads 254.
The problem with
method 200 is that when
method 200 is applied to a semiconductor wafer that includes an aluminum fuse and an aluminum fuse target, the chemistry used to remove the un-used regions of
seed layer 222 also attacks the exposed aluminum of the fuse target. As a result, following the formation of a layer of copper traces, the exposed aluminum of the fuse target, such as
fuse target 120, can be damaged to the point of where the optical recognition system can no longer detect the fuse target. When this occurs, the position of the fuse can no longer be identified, and the fuse can no longer be programmed.
As a result, there is a need for a fuse target that is compatible with the current-generation fabrication processes that are used to form copper-topped interconnect structures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1C are views illustrating a prior-
art semiconductor wafer 110 with a fuse and a fuse target.
FIG. 1A is a plan view, while
FIGS. 1B and 1C are cross-sectional views taken along
line 1B-
1B of
FIG. 1A.
FIGS. 2A-2G are a series of cross-sectional views illustrating a prior-
art method 200 of forming a layer of copper traces.
FIGS. 3A-3K are a series of cross-sectional views illustrating a
method 300 of forming a fuse target in accordance with the present invention.
FIG. 4A is a plan view illustrating a region of
semiconductor wafer 310 in accordance with the present invention.
FIG. 4B is a plan
view illustrating wafer 310 following the removal of
mask 354 in accordance with the present invention.
FIGS. 5A-5K are a series of cross-sectional views illustrating a
method 500 of forming a copper-compatible fuse target in accordance with an alternate embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 3A-3K show a series of cross-sectional views that illustrate a
method 300 of forming a fuse target in accordance with the present invention. As shown in
FIG. 3A,
method 300 utilizes a conventionally-formed
semiconductor wafer 310. In the present example,
semiconductor wafer 310 is identical to
semiconductor wafer 110 except that
semiconductor wafer 310 utilizes a
metal interconnect structure 312 in lieu of
metal interconnect structure 114.
Metal interconnect structure 312, in turn, is identical to
metal interconnect structure 114 except that
metal interconnect structure 312 utilizes a to-be-described copper-based fuse target in lieu of
fuse target 120. As a result, the reference numerals of
semiconductor wafer 310 that match the reference numerals of
semiconductor wafer 110 identify the same structures as the reference numerals of
semiconductor wafer 110.
As shown in
FIG. 3A,
method 300 begins by forming and patterning a
mask 316 on the
top surface 114S of
passivation layer 114U. Following this, the exposed regions of
passivation layer 114U are etched to form a number of
passivation openings 320 that expose the top surfaces of the aluminum metal-4 traces
114-M
4. (Only one
passivation opening 320 is shown for clarity.) The etch also forms
opening 118.
Mask 316 is then removed.
As shown in
FIG. 3B, after
mask 316 has been removed, a
seed layer 322 is formed on
insulation region 114I, and the exposed regions of the aluminum metal-4 traces
114-M
4.
Seed layer 322 typically includes a layer of titanium (e.g., 300 Å thick) and an overlying layer of copper (e.g., 3000 Å thick). The titanium layer enhances the adhesion between the underlying aluminum trace
114-M
4 and the overlying layer of copper.
After
seed layer 322 has been formed, a
mask 324 is formed and patterned on
seed layer 322 to have a number of conducting
openings 326 that expose the number of
passivation openings 320, and to also have a number of
target openings 328, e.g., one in each corner of a region that surrounds the fuse banks.
As shown in
FIG. 3C, following the formation and patterning of
mask 324, copper is electroplated to form a number of spaced-apart copper traces
330 in the
openings 320 and
326, and a number of electrically-isolated
copper targets 332 in the
openings 328. As a result, the copper traces
330 are electrically connected to the top surfaces of the aluminum metal-4 traces
114-M
4 by way of
seed layer 322. Further, each of the copper traces
330 has a
top surface 330T, and each of the copper targets
332 has a
top surface 332T. (Only one
copper trace 330 and one
copper target 332 are shown for clarity.)
Mask 324 and the
seed layer 322 that underlies
mask 324 are then removed. As shown in
FIG. 3D, the removal of
seed layer 322 defines a number of
seed portions 322P that contact the top surfaces of the aluminum metal-4 traces
114-M
4,
passivation layer 114U, and the copper traces
330. The removal of
seed layer 322 also defines a number of spaced apart
seed targets 322T that
contacts passivation layer 114U and the copper targets
332. (Only one
seed portion 322P and one
seed target 322T are shown for clarity.)
After
mask 324 and
seed layer 322 have been removed, a layer of
non-conductive material 340 is deposited on
passivation layer 114U, the copper traces
330, and the copper targets
332.
Non-conductive layer 340 can be implemented with, for example, benzocyclobutene (BCB) or a polymer.
In the present example, once
non-conductive layer 340 has been formed, as shown in
FIG. 3E,
non-conductive layer 340 is planarized until the
top surfaces 330T of the copper traces
330 and the
top surfaces 332T of the copper targets
332 have been exposed, thereby forming a planarized
non-conductive layer 340P. (Other examples are discussed below.) Thus, as shown in the
FIG. 3E example, the
top surface 330T of each of
copper trace 330, the
top surface 332T of each
copper target 332, and a
top surface 340T of planarized
non-conductive layer 340P lie in a common horizontal plane CP.
Following this, as shown in
FIG. 3F, a
metal plate 344 is formed on the
top surface 330T of each
copper trace 330, and a
metal target 346 is formed on the
top surface 332T of each
copper target 332. As shown, the
metal plates 344 and the
metal targets 346, which are thin flat layers, are identical except that the
metal plates 344 are larger than the
top surfaces 330T of the copper traces
330, while the
metal targets 346 are smaller than the
top surfaces 332T of the copper targets
332.
FIG. 4A shows a plan view that illustrates a region of
semiconductor wafer 310 in accordance with the present invention. As shown in
FIG. 4A, the top surface of a
metal plate 344A has an area AR
1 measured in the common plane CP (which lies parallel to the surface of the page), while the top surface of a
copper trace 330A has an area AR
2 measured in the common plane CP that is smaller than the area AR
1 of
metal plate 344A.
By forming
metal plate 344A to be larger than the top surface of the
copper trace 330A, the need for a sealant can be eliminated. On the other hand, as described in greater detail below, each
copper target 332 is part of a to-be-formed fuse target and, as a result, need not be sealed. As a result, the area (measured in the common plane CP) of
metal target 346 is less than the area (measured in the common plane CP) of
copper target 332 by an amount which is sufficient to ensure that, within the maximum misalignment error,
metal target 346 is completely formed on the
top surface 332T of
copper target 332.
Referring to
FIG. 3G, the
metal plates 344 and the
metal targets 346 can be formed by depositing a
metallic layer 350, such as a layer of aluminum, aluminum-copper, or gold (and can optionally include an underlying layer of material, such as titanium, which improves the adhesion of the metallic layer to copper), on planarized
non-conductive layer 340P, the copper traces
330, and the copper targets
332. When
metallic layer 350 is formed with aluminum-copper,
metallic layer 350 has more than 50% aluminum, such as aluminum with 0.5% copper.
Following the formation of
metallic layer 350, a
mask 352 is formed and patterned on
metallic layer 350. Once
mask 352 has been patterned, as shown in
FIG. 3H, the exposed regions of
metallic layer 350 are etched away to form the
metal plates 344 and the metal targets
346.
Mask 352 is then removed.
In accordance with the present invention, a
seed target 322T, a
copper target 332 that lies over and touches the
seed target 322T, and a
metal target 346 that lies over and touches the
copper target 332 form a
fuse target 360 that is electrically isolated from all other conducting regions.
After
mask 352 has been removed, as shown in
FIG. 3I, a
mask 354 is formed and patterned on
non-conductive layer 340P, the
metal plates 344, and the fuse targets
360. Once
mask 354 has been formed and patterned, as shown in
FIG. 3J, the exposed regions of planarized
non-conductive layer 340P are etched to re-open
fuse opening 118. At the same time, the exposed regions of
non-conductive layer 340P that lie around each
fuse target 360 are etched away. The etch forms a number of
trenches 362 that each surrounds a
copper target 332 and exposes the
side wall 332S of the
copper target 332.
One of the advantages of the present invention is that, as shown in
FIG. 3J,
passivation layer 114U functions as an etch stop which prevents the etch which re-opens fuse opening
118 from etching into the
planarized insulation region 114I that lies below
fuse target 360. Thus, because
fuse target 360 lies above
passivation layer 114U, the need for stacked metal ring structure MR
2 is eliminated.
As noted above, stacked metal ring structure MR
2 is formed around
fuse target 120 shown in
FIGS. 1A-1C to protect adjacent regions of
wafer 110 from the etch that forms fuse
trench 124. In the present invention,
passivation layer 114U prevents a fuse trench like
fuse trench 124 from being formed. As a result, there is no need for stacked metal ring structure MR
2. The elimination of stacked metal ring structure MR
2, in turn, increases the space available for other metal interconnect structures.
As shown in
FIG. 3K,
mask 354 is then removed to complete
method 300 of the present invention. Alternately, after
mask 354 has been removed,
solder balls 370 can next be attached to selected regions on the top surfaces of the
metal plates 344 as illustrated in
FIG. 3K or,
thin wires 372 can next be bonded to selected regions on the top surfaces of the
metal plates 344 as alternately illustrated in
FIG. 3K.
FIG. 4B shows a plan view that illustrates
wafer 310 following the removal of
mask 354 in accordance with the present invention. As shown in
FIGS. 1A and 4B, the view of
fuse target 120 and the view of
fuse target 360 are substantially identical as seen from the perspective of the optical recognition system. As a result,
fuse 116 in
wafer 310 is programmed in the same manner as
fuse 116 in
wafer 110. (The optical recognition system may need to be compensated to accommodate any changes in the vertical separation distance between the fuse target and the optical recognition system.)
In an alternate embodiment, the method of the present invention can include the sealing steps illustrated in
FIG. 2D or
2E.
FIGS. 5A-5K show a series of cross-sectional views that illustrate a
method 500 of forming a fuse target in accordance with an alternate embodiment of the present invention.
Method 500, when practiced on
wafer 310 shown in
FIG. 3A, is the same as
method 300 up through the formation of the copper traces
330 and the copper targets
332.
Method 500 then follows the process described above with respect to
FIG. 2D or
2E, to form the sealed copper traces and the sealed copper targets.
With respect to
FIG. 2D, once the copper traces
330 and the copper targets
332 have been formed,
mask 324 and the
underlying seed layer 322 are removed. The removal of
seed layer 322 defines the
seed portions 322P that contact the top surfaces of the aluminum metal-4 traces
114-M
4,
passivation layer 114U, and the copper traces
330. The removal of
seed layer 322 also defines the
seed targets 322T that
contact passivation layer 114U and the copper targets
332.
As shown in
FIG. 5A, after
mask 324 and the
seed layer 322 that underlies
mask 324 have been removed, a
sealant layer 510 that is resistant to humidity and corrosion, such as cobalt or nickel, is deposited on
passivation layer 114U, the copper traces
330, and the copper targets
332. Following this, a
mask 512 is formed and patterned on
sealant layer 510.
The exposed regions of
sealant layer 510 are then removed from the top surface of
passivation layer 114U to form a number of spaced-apart
sealant portions 510P and a number of spaced-apart
sealant targets 510T. (Only one
sealant portion 510P and one
sealant target 510T are shown for clarity.) A
sealant portion 510P and an
underlying copper trace 330, in turn, define a sealed
copper trace 514, while a
sealant target 510T and an
underlying copper target 332 define a sealed
copper target 516. Each sealed
copper trace 514, which has a
top surface 514T, sits on a
seed portion 322P. Each sealed
copper target 516, which has a
top surface 516T, sits on a
seed target 322T.
Mask 512 is then removed.
Alternately, as shown in
FIG. 5B,
mask 324 can be removed, followed by the deposition of
sealant layer 510 over
seed layer 322, the copper traces
330, and the copper targets
332.
Mask 512 is then formed as above. After this, the exposed regions of
sealant layer 510 and the
underlying seed layer 322 are then removed from the top surface of
passivation layer 114U to form the
sealant portions 510P, the sealed copper traces
514, and the
seed portions 322P. In addition, the etch also forms the sealant targets
510T, the sealed
copper targets 516, and the seed targets
322T.
Mask 512 is then removed.
Next, as shown in
FIG. 5C,
non-conductive layer 340 is formed on the sealed copper traces
514 and the sealed copper targets
516. Once
non-conductive layer 340 has been formed, as shown in
FIG. 5D, in a first variation,
non-conductive layer 340 is planarized until the
top surfaces 514T of the sealed copper traces
514 and the
top surface 516T of the sealed
copper targets 516 have been exposed to form planarized
non-conductive layer 340P. Thus, as shown in
FIG. 5D, the
top surface 514T of each sealed
copper trace 514, the
top surface 516T of each sealed
copper target 516, and a
top surface 340T of planarized
non-conductive layer 340P lie in the common horizontal plane CP.
Following this, as shown in
FIG. 5E, a number of
metal bond pads 520 are formed over selected regions of the
top surfaces 514T of the sealed copper traces
514, and a number of
metal targets 522 are formed over the sealed copper targets
516. In the alternate embodiment, a
seed target 322T, a sealed
copper target 516 that lies over and touches the
seed target 322T, and a
metal target 522 that lies over and touches the
copper target 332 form a
fuse target 530 that is electrically isolated from all other conducting regions.
The
metal bond pads 520 differ from the
metal plates 344 in that the
metal bond pads 520 are formed over selected regions of the
top surfaces 514T of the sealed copper traces
514 rather than over all of the copper traces, and are formed to be less than the same size as the selected regions of the
top surfaces 514T of the sealed copper traces
514. Since the copper traces are sealed, the
metal bond pads 520 need not cover all of the copper traces, and need not be larger than the selected regions of the
top surfaces 514T of the sealed copper traces
514 to provide sealing, but can be smaller to accommodate any misalignment error. The metal targets
522, in turn, are substantially identical to the metal targets
346.
As shown in
FIG. 4A, the top surface of a
metal bond pad 520A can have an area AR
3 that is less than an area AR
4 of the top surface of a sealed
copper trace 514A.
Metal bond pads 520 allow a greater density of metal traces to be used.
Referring to
FIG. 5F, after the
metal bond pads 520 and the
metal targets 522 have been formed, a
mask 354 is formed and patterned on
non-conductive layer 340P, the
metal bond pads 520, and the fuse targets
530. Once
mask 354 has been formed and patterned, as shown in
FIG. 5G, the exposed regions of planarized
non-conductive layer 340P are etched to re-open
fuse opening 118.
At the same time, the exposed regions of
non-conductive layer 340P that lie around each
fuse target 530 are etched away. The etch forms a number of
trenches 532 that surrounds the sealed
copper targets 516 and exposes the
side walls 516S of the sealed copper targets
516. As shown in
FIG. 5H,
mask 354 is then removed to complete
method 500 of the present invention. Alternately, after
mask 354 has been removed, solder balls can next be attached to the
metal bond pads 520 or, thin wires can next be bonded to the
metal bond pads 520.
As noted above, in a first variation,
non-conductive layer 340 is planarized as shown in
FIG. 5D. In a second variation, as shown in
FIG. 5I, after second
non-conductive layer 340 has been deposited, a
mask 540 is formed on
non-conductive layer 340. Following this, the exposed regions of
non-conductive layer 340 are etched to form
openings 542 that expose the sealed copper traces
514 and the sealed copper targets
516.
Mask 540 is then removed.
As shown in
FIG. 5J, after the
openings 542 in
non-conductive layer 340 have been formed, a
metal layer 544, such as aluminum, aluminum-copper, or gold (and can optionally include an underlying layer of material, such as titanium, which improves the adhesion of the metallic layer to sealed copper), is deposited on
non-conductive layer 340 to fill up the
openings 542 and contact the sealed copper traces
514 and the sealed copper targets
516. After this, a
mask 546 is formed and patterned on
metal layer 544. Next, the exposed regions of
metal layer 544 are etched to form a number of
metal bond pads 550 and a number of metal targets
552.
Mask 546 is then removed.
In the second version, a
seed target 322T, a sealed
copper target 516 that lies over and touches the
seed target 322T, and a
metal target 552 that lies over and touches the sealed
copper target 516 form a
fuse target 554 that is electrically isolated from all other conducting regions.
After
mask 546 has been removed, as shown in
FIG. 5K, a
mask 556 is formed and patterned on
non-conductive layer 340, the
bond pads 550, and the metal targets
552. Once
mask 556 has been formed and patterned, the exposed region of planarized
non-conductive layer 340 is etched to re-open
fuse opening 118.
At the same time, the exposed regions of
non-conductive layer 340 that lie around each
fuse target 554 are etched away. The etch forms a number of
trenches 560 that surrounds the sealed
copper targets 516 and exposes the
side walls 516S of the sealed copper targets
516.
Mask 556 is then removed to complete
method 500 of the present invention. Alternately, after
mask 556 has been removed, solder balls can next be attached to the
metal bond pads 550 or, thin wires can next be bonded to the
metal bond pads 550.
Thus, a method of forming a fuse target has been described. As shown in
FIG. 3K,
semiconductor wafer 310 has an
isolation structure 380 that includes
passivation layer 114U and
non-conductive layer 340P. In addition,
isolation structure 380 has a
top surface 380T, a number of
isolation openings 380P that expose the aluminum traces
114-M
4, and a number of
target openings 380T that expose no conducting region. (Only one
isolation opening 380P and one
target opening 380T are shown for clarity.)
As shown in
FIG. 3K,
wafer 310 also has a number of
connection structures 382 that lie in the
isolation openings 380P and touch the
isolation structure 380 and the aluminum traces
114-M
4. Each
connection structure 382 has a
top surface 382T. A
connection structure 382 can be implemented with a
seed portion 322P and an
overlying copper trace 330, or with a
seed portion 322P, an overlying
copper trace 330, and an
overlying sealant portion 510P.
Wafer 310 also has a
target structure 384 that lies in
target opening 380T.
Target structure 384 has a
top surface 384T, and can be implemented with a
seed target 322T and a
copper target 332, or with a
seed target 322T, a
copper target 322, and a
sealant target 510T. In the present invention, as shown in
FIG. 3E, the
top surface 382T of each
connection structure 382, the
top surface 384T of each
target structure 384, and the
top surface 380T of the
isolation structure 380 lie in the common plane CP.
Further, as shown in
FIG. 3K,
wafer 310 has a number of spaced-apart
metal plates 344 and a number of spaced-apart metal targets
346. (One
only plate 344 and one
target 346 are shown for clarity.) The
metal plates 344 touch the
top surfaces 382T of the
connection structures 382. The metal targets
346 touch the
top surfaces 384T of the
target structures 384. A
target structure 384 and a
metal target 346 define
fuse target 360, which is electrically isolated from all other conducting regions.
It should be understood that the above descriptions are examples of the present invention, and that various alternatives of the invention described herein may be employed in practicing the invention. Thus, it is intended that the following claims define the scope of the invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.